Golf ball compositions

ABSTRACT

The present invention relates to improved cover compositions for golf ball construction. The cover compositions comprise a blend of (1) modified thermoplastic rubber elastomers, wherein the thermoplastic rubber elastomers are modified with a polar group, such as maleic anhydride, and (2) ionomer resins.  In addition, the present invention is directed to golf balls produced utilizing the improved cover compositions. The golf balls exhibit properties of enhanced playability without sacrificing distance and/or durability.

BACKGROUND OF THE INVENTION

The present invention is directed to improved golf ball covercompositions suitable for golf ball construction. More particularly, thepresent invention relates to novel golf ball compositions comprised of ablend of ionomeric resins and thermoplastic rubber elastomers modifiedwith various polar groups.

In addition, the present invention is directed to golf balls producedutilizing the improved cover compositions. The golf balls exhibitproperties of enhanced playability without sacrificing distance and/ordurability.

Ionomeric resins are polymers containing interchain ionic bonding. As aresult of their toughness, durability, and flight characteristics,various ionomeric resins sold by E.I. DuPont deNemours & Company underthe trademark "Surlyn®" have become the materials of choice for theconstruction of golf ball covers over the traditional "balata" (transpolyisoprene, natural or synthetic) rubbers. The softer balata covers,although exhibiting enhanced playability properties, lack the durabilitynecessary for repetitive play.

Ionomeric resins are generally ionic copolymers of an olefin such asethylene and a metal salt of an unsaturated carboxylic acid, such asacrylic acid, methacrylic acid, or maleic acid. Metal ions, such assodium or zinc, are used to neutralize some portion of the acidic groupsin the copolymer resulting in a thermoplastic elastomer exhibitingenhanced properties, i.e. durability, etc. for golf ball coverconstruction over balata. However, the advantages gained in increaseddurability have been offset to some degree by the decreases produced inplayability.

While there are currently more than fifty commercial grades of ionomersavailable from DuPont with a wide range of properties which varyaccording to the type and amount of metal cations, molecular weight,composition of the base resin (i.e. relative content of ethylene andmethacrylic acid groups) and additive ingredients such as reinforcementsor additives, a great deal of research continues in order to developgolf ball cover compositions exhibiting not only the enhanced impactresistance and carrying distance properties produced by the "hard"ionomeric resins, but also the playability (i.e. "spin") characteristicspreviously associated with the "soft" balata covers, properties whichare still desired by the more skilled golfer. Thus, an object of thepresent invention is to provide golf ball cover compositions which, whenutilized in golf ball construction, produce golf balls exhibitingimproved playability properties while maintaining satisfactoryresilience and durability.

As is indicated in U.S. Pat. No. 4,674,751, the patent literature isreplete with proposed cover formulations seeking to improve upon thebalata and ionomer covers which have been commercially successful, i.e.see U.S. Pat. Nos. 3,819,768; 3,359,231; 4,398,000; 4,234,184;4,295,652; 4,248,432; 3,989,568; 3,310,102; 4,337,947; 4,123,061, and3,490,246. However, none of these patents disclose and/or suggest theparticular compositions of the present invention and the improvedcharacteristics produced by golf balls formulated with suchcompositions.

The present invention is directed to new golf ball cover compositionswhich exhibit properties of enhanced playability (i.e. softness andspin) without sacrificing carrying distance (i.e. coefficient ofrestitution) and/or durability. It has been found that these propertiescan be produced by using ionomeric resins in combination withthermoplastic rubber elastomers modified with various polar groups, suchas maleic anhydride. Along this line, the present inventor discoveredthat contrary to the previous research in this area, the addition ofnewly developed polar modified thermoplastic rubbers to ionomeric resincompositions greatly improves the playability properties (i.e. decreasesthe hardness and increases the spin) of the compositions withoutadversely affecting the desired properties (i.e. cut resistance and/orresilience) produced by ionomeric resins.

SUMMARY OF THE INVENTION

The present invention is directed to improved golf ball covercompositions and the resulting golf balls produced utilizing the covercompositions. The novel golf ball cover compositions of the inventioncomprise a blend of (1) thermoplastic rubber elastomers modified with apolar group, such as maleic anhydride, and (2) ionomeric resins. Whenthe cover compositions of the invention are utilized to manufacture golfballs, the golf balls produced exhibit properties of improvedplayability without sacrificing distance and/or durability.

Two of the principal properties involved in the performance of golfballs are resilience and hardness. Resilience is determined by thecoefficient of restitution (C.O.R.), the constant "e", which is theratio of the relative velocity of two elastic spheres after directimpact to that before impact. As a result, the coefficient ofrestitution (i.e. "e") can vary from zero to one, with one beingequivalent to an elastic collision and zero being equivalent to aninelastic collision.

Resilience (C.O.R.), along with additional factors such as clubheadspeed, angle of trajectory, and ball configuration (i.e. dimplepattern), generally determines the distance a ball will travel when hit.Since clubhead speed and the angle of trajectory are not factors easilycontrollable, particularly by golf ball manufacturers, the factors ofconcern among manufacturers are the coefficient of restitution (C.O.R.)and the surface configuration of the ball.

The coefficient of restitution (C.O.R.) in solid core balls is afunction of the composition of the molded core and of the cover. Inballs containing a wound core (i.e. balls comprising a liquid or solidcenter, elastic windings, and a cover), the coefficient of restitutionis a function of not only the composition of the center and cover, butalso the composition and tension of the elastomeric windings. Althoughboth the core and the cover contribute to the coefficient ofrestitution, the present invention is directed solely to the coefficientof restitution which is affected by the cover composition.

In this regard, the coefficient of restitution of a golf ball isgenerally measured by propelling a ball at a given speed against a hardsurface and measuring the ball's incoming and outgoing velocityelectronically. As mentioned above, the coefficient of restitution isthe ratio of the outgoing velocity to incoming velocity. The coefficientof restitution must be carefully controlled in all commercial golf ballsin order for the ball to be within the specifications regulated by theUnited States Golf Association (U.S.G.A.). Along this line, the U.S.G.A.standards indicate that a "regulation" ball cannot have an initialvelocity (i.e. the speed off the club) exceeding 255 feet per second.Since the coefficient of restitution of a ball is related to the ball'sinitial velocity, it is highly desirable to produce a ball having asufficiently high coefficient of restitution to closely approach theU.S.G.A. limit on initial velocity, while having an ample degree ofsoftness (i.e. hardness) to produce enhanced playability (i.e. spin,etc.).

The hardness of the ball is the second principal property involved inthe performance of a golf ball. The hardness of the ball can affect theplayability of the ball on striking and the sound or "click" produced.Hardness is determined as the deformation (i.e. compression) of the ballunder various load conditions applied across the ball's diameter (i.e.the lower the compression value, the harder the material). As indicatedin U.S. Pat. No. 4,674,751, "softer" covers permit the accomplishedgolfer to impart proper spin. This is because the softer covers deformon impact significantly more than balls having "harder" ionomeric resincovers. As a result, this allows the better player to impart fade, draw,or backspin to the ball thereby enhancing playability. Such propertiescan be determined by various "spin rate tests", such as the "nine-iron"spin rate test set forth below.

Accordingly, the present invention is directed to new cover compositionswhich produce, upon molding around solid or wound cores, golf ballsexhibiting a sufficient amount of hardness (i.e. softness) to improvethe playability of the balls without adversely affecting the ball'sdistance (i.e. resilience) and/or durability (i.e. impact resistance,etc.).

These and other objects and features of the invention will be apparentfrom the following description and from the claims.

DESCRIPTION OF THE INVENTION

The present invention relates to improved cover compositions for golfball construction. The cover compositions comprise a blend of (1)modified thermoplastic rubber elastomers, wherein the thermoplasticrubber elastomers are modified with a polar group, such as maleicanhydride, and (2) ionomer resins.

The thermoplastic rubber elastomers suitable for use in the presentinvention include modified copolymers of ethylene and propylene (i.e.ethylene-propylene rubbers (EPR)) and styrenic block copolymers.Styrenic block copolymers are manufactured in the U.S. by The ShellChemical Co. and marketed under the tradenames of "Kraton D Rubber"(i.e. styrene-butadiene-styrene (SBS) and styrene-isoprene-styrene (SIStypes)), and "Kraton G Rubber" (i.e. styrene-ethylene-butylene-styrene(SEBS) and styrene-ethylene-propylene-styrene (SEPS)).

In this regard, it has been discovered that thermoplastic rubbers whichhave been modified with a polar group, such as a newly developed maleicanhydride modified thermoplastic rubber sold by the Shell Chemical Co.under the designation "Kraton FG 1901X", are particularly well suitedfor use in golf ball cover construction. When the Kraton FG 1901X maleicanhydride modified thermoplastic rubber is blended with the specificionomeric resins at the proportions set forth below and applied to asolid core to produce a molded golf ball, noticeable improvements inplayability (i.e. spin properties, etc.) of the ball are producedwithout sacrificing the ball's durability (i.e. impact resistance,etc.), and/or resilience (coefficient of restitution) which relatesdirectly to the distance that a golf ball will travel when struck undercontrolled conditions.

This is a particularly interesting discovery in that when the presentinventor had previously attempted to blend the softer unmodifiedthermoplastic rubber elastomers with the harder ionomeric resins inorder to improve the playability of the balls, the blends of theunmodified thermoplastic rubber-ionomeric resins suffered frominadequate compatibility, and thus produced covers which exhibited verypoor durability (i.e. inadequate impact resistance). It was only whenthe thermoplastic rubber elastomers had been modified with a polargroup, such as maleic anhydride, and blended with the relatively hardionomeric resins, were improvements in both playability and durabilityexhibited. This is because it is believed that the polar or maleicanhydride group interacts (i.e. forms hydrogen bonds, etc.) with theacid groups of the ionomeric resins to produce a more compatible andhomogenous mixture than the unmodified thermoplastic rubbers.

The maleic anhydride functionalized styrene block copolymers recentlydeveloped by the Shell Chemical Co. have been found to be particularlywell suited for use in the present invention. Although these newcopolymers have been used to generate super-tough blends with nylons,polyethylene terephthalate (PET), and PBT, and are also useful forcompatible blends of dissimilar polymers, it was unknown until thedevelopment of the present invention that the modified styrenic blockcopolymers could be blended with ionomer resins in order to producecompositions useful for golf ball cover construction. As a result,Kraton FG 1901X thermoplastic rubber, which is a maleicanhydride-functionalized triblock copolymer consisting of polystyreneend blocks and poly(ethylene/butylene) (i.e.styrene-ethylene-butylene-styrene block copolymer (SEBS)) has beenproven by the present inventor(s) to be an effective additive forionomeric resin cover blends.

Shown in Table 1 below is a comparison of the mechanical properties ofKraton FG 1901X with "Kraton 1101", "Kraton G-2701", and "KratonG-2706X", three unmodified styrene-diene thermoplastic block copolymerssold by the Shell Chemical Co.

                  TABLE 1                                                         ______________________________________                                        Typical Properties of Modified and Unmodified                                 Styrene-Diene Block Copolymers                                                                  Kraton  Kraton   Kraton                                               Kraton  1101    G-2701   G-2706X                                              FG 1901X                                                                              (SBS)   (SEBS)   (SEBS)                                     ______________________________________                                        Specific    0.91      0.94    0.90   0.90                                     Gravity (g/cc)                                                                Polymeric   28        30      NA     NA                                       Styrene Content                                                               (% weight)                                                                    Functionality                                                                             2         --      --     --                                       (% weight as                                                                  bound maleic                                                                  anhydride)                                                                    Hardness,   75        71      67     28                                       Shore A                                                                       Tensile     5,000     4,611   1,600  850                                      Strength, psi                                                                 Elongation at                                                                             500       880     260    950                                      Break, %                                                                      ______________________________________                                    

Furthermore, additional modified thermoplastic rubbers suitable for usein the present invention include other maleic anhydride modifiedthermoplastic rubbers currently under development by the Shell ChemicalCo. under the "Kraton" designation. Examples of these additionalmodified thermoplastic rubbers include Kraton RP-6510 (containing about0.5 weight % maleic anhydride (MA)), Kraton RP-52-14 (containing about2.5 weight % maleic anhydride (MA)), Kraton RP-6505 (containing about1.0% weight % maleic anhydride (MA)) and others listed below in Table 2.In this regard, Table 2 compares the variable differences of a largenumber of developmental maleic anhydride functionalized block copolymersto that of Kraton FG 1901X.

                  TABLE 2                                                         ______________________________________                                        Variable Differences in Developmental Maleic Anhydride                        Functionalized Block Copolymers Relative                                      to Kraton FG 1901X                                                            Develop-                             %                                        mental   %      Block Mole Wt.                                                                              Wt %   3 Block                                  Polymer  MA     Styrene  Rubber Styrene                                                                              Polymer                                ______________________________________                                        RP 52-14 2.5    NC       NC     NC     NC                                     RP 6505  1.0    NC       NC     NC     NC                                     RP 6510  0.5    NC       NC     NC     NC                                     RP 50-1  NC     +        +      NC     NC                                     RP 50-3  +      +        +      NC     NC                                     RP 50-6  -      +        +      NC     NC                                     RP 6509  -      -        +VA    -      -                                      RP 6511-1                                                                              --     ++       ++     ++     --                                     RP 6511-2                                                                              -      ++       ++     ++     --                                     RP 6511-3                                                                              -      ++       ++     ++     --                                     ______________________________________                                         NC = No Change                                                                - = Decrease                                                                  + = Increase                                                                  VS = Very Slight                                                         

These additional modified thermoplastic rubbers, when used in theproportions and combinations set forth below to formulate golf ballcover compositions, produce golf balls exhibiting enhanced coefficientof restitution and durability without adversely affecting theplayability of the balls.

In addition, it has recently been observed that the modifiedthermoplastic rubbers suitable for use in the present invention may alsobe blended with unmodified thermoplastic rubbers and ionomeric resins toproduce golf balls exhibiting an increase in the coefficient ofrestitution (i.e. rebound) while maintaining the balls's overallplayability characteristics. Along this line, it is believed that themodified thermoplastic rubbers act as a compatibilizer between theunmodified thermoplastic rubbers and the ionomeric resins. Since theunmodified thermoplastic rubbers are less costly than the modifiedthermoplastic rubbers, this observation offers many commercialadvantages.

The ionomeric resins utilized to produce the cover compositions may bemade according to known procedures such as those in U.S. Pat. No.3,421,766 or British Patent No. 963,380, with neutralization effectedaccording to procedures disclosed in Canadian Patent Nos. 674,595 and713,631, wherein the ionomer is produced by copolymerizing the olefinand carboxylic acid to produce a copolymer having the acid unitsrandomly distributed along the polymer chain. The ionic copolymercomprises one or more α-olefins and from about 9 to about 20 weightpercent of α, β-ethylenically unsaturated mono- or dicarboxylic acid,the basic copolymer neutralized with metal ions to the extent desired.

At least 20% of the carboxylic acid groups of the copolymer areneutralized by the metal ions, such as sodium, potassium, zinc, calcium,magnesium, and the like, and exist in the ionic state.

Suitable olefins for use in preparing the ionomeric resins include, butare not limited to, ethylene, propylene, butene-1, hexene-1, and thelike. Unsaturated carboxylic acids include, but are not limited toacrylic, methacrylic, ethacrylic, α-chloroacrylic, crotonic, maleic,fumaric, itaconic acids, and the like. Preferably, the ionomeric resinis a copolymer of ethylene with acrylic and/or methacrylic acid. Inaddition, two or more types of ionomeric resins may be blended into thecover compositions in order to produce the desired properties of theresulting golf balls.

Although the scope of the patent embraces all known ionomeric resinssuitable for use in the present invention, only a relatively limitednumber of these ionomeric resins are commercially available. In thisregard, the ionomeric resins sold by E.I. DuPont de Nemours Companyunder the trademark "Surlyn®", and the ionomer resins sold by ExxonCorporation under either the trademark "Escor®" or the tradename "Iotek"are examples of commercially available ionomeric resins which may beutilized in the present invention in the combinations described indetail below. The ionomeric resins sold formerly under the designation"Escor®" and now under the new name "Iotek", are very similar to thosesold under the "Surlyn®" trademark in that the "Iotek" ionomeric resinsare available as sodium or zinc salts of poly(ethylene acrylic acid) andthe "Surlyn" resins are available as zinc or sodium salts ofpoly(ethylene methacrylic acid). In addition, various blends of "Iotek"and "Surlyn" ionomeric resins, as well as other available ionomericresins, may be utilized in the present invention.

Examples of commercially available ionomeric resins which may beutilized in the present invention include the sodium ionic copolymersold under the trademark "Surlyn 8940" and the zinc ionic copolymer soldunder the trademark "Surlyn 9910". Surlyn 8940 is a copolymer ofethylene with methacrylic acid with about 15 weight percent acid whichis about 29% neutralized with sodium ions. This resin has an averagemelt flow index of about 2.8. Surlyn 9910 is a copolymer of ethylene andmethacrylic acid with about 15 weight percent acid which is about 58%neutralized with zinc ions. The average melt flow index of Surlyn 9910is about 0.7. The typical properties of Surlyn 9910 and 8940, as well asadditional ionomeric resins which may be utilized in the presentinvention, are set forth below in Table 3.

                                      TABLE 3                                     __________________________________________________________________________    Typical Properties of Commercially Available                                  Surlyn Resins Suitable for Use in the Present Invention                                   ASTM D                                                                             9910 8940  AD-8265                                                                            AD-8269                                      __________________________________________________________________________    Cation Type      Sodium                                                                             Zinc  Sodium                                                                             Sodium                                       Melt flow index,                                                                          D-1238                                                                             2.8  0.7   0.9  0.9                                          gms/10 min.                                                                   Specific Gravity,                                                                         D-792                                                                              0.95 0.97  0.94 0.94                                         g/cm.sup.3                                                                    Hardness, Shore A/D                                                                       D-2240                                                                             --/66                                                                              --/64 92/39                                                                              84/25                                        Tensile Strength,                                                                         D-638                                                                              (4.8) 33.1                                                                         (3.6) 24.8                                                                          (4.2) 28.8                                                                         (3.1) 21.2                                   (kpsi), MPa                                                                   Elongation, %                                                                             D-638                                                                              470  290   660  770                                          Flexural Modulus,                                                                         D-790                                                                              (51) 350                                                                           (48) 330                                                                            (7.1) 49.1                                                                         (2.8) 19.3                                   (kpsi) MPa                                                                    Tensile Impact (23° C.)                                                            D-18225                                                                            760 (360)                                                                          1010 (480)                                                                          494 (235)                                                                          447 (213)                                    KJ/m.sub.2 (ft.-lbs./in.sup.2)                                                Melting Point, °C.                                                                 DTA  --   --    81   72                                           Freezing Point, °C.                                                                DTA  --   --    51   38                                           Vicat Temperature, °C.                                                             D-1525                                                                             63   62    51   48                                           __________________________________________________________________________

In addition, examples of ionomer resins suitable for use in the presentinvention sold under the "Iotek" tradename by the Exxon Corporationinclude "Iotek 4000" (formerly "Escor 4000"), "Iotek 4010", "Iotek 4000"(formerly Escor 900), "Iotek 8020", and "Iotek 8030". The typicalproperties of the Iotek ionomers are set forth below in Table 4.

                                      TABLE 4                                     __________________________________________________________________________    Typical Properties of Iotek Ionomers                                                        ASTM                                                                          Method                                                                             Units                                                                              4000                                                                              4010                                                                              8000                                                                              8020                                                                              8030                                  __________________________________________________________________________    Resin                                                                         Properties                                                                    Cation type             zinc                                                                              zinc                                                                              sodium                                                                            sodium                                                                            sodium                                Melt index    D-1238                                                                             g/10 min.                                                                            2.5                                                                               1.5                                                                               0.8                                                                               1.6                                                                               2.8                                 Density       D-1505                                                                             kg/m.sup.3                                                                         963 963 954 960 960                                   Melting Point D-3417                                                                             °C.                                                                         90  90  90    87.5                                                                              87.5                                Crystallization Point                                                                       D-3417                                                                             °C.                                                                         62  64  56  53  55                                    Vicat Softening Point                                                                       D-1525                                                                             °C.                                                                         62  63  61  64  67                                    Plaque                                                                        Properties                                                                    (3 mm thick,                                                                  compression molded)                                                           Tensile at break                                                                            D-638                                                                              MPa  24  26  36    31.5                                                                            28                                    Yield point   D-638                                                                              MPa  none                                                                              none                                                                              21  21  23                                    Elongation at break                                                                         D-638                                                                              %    395 420 350 410 395                                   1% Secant modulus                                                                           D-638                                                                              MPa  160 160 300 350 390                                   Shore Hardness D                                                                            D-2240                                                                             --   55  55  61  58  59                                    Film Properties                                                               (50 micron film 2.2:1                                                         Blow-up ratio)                                                                Tensile at Break                                                                         MD D-882                                                                              MPa  41  39  42  52    47.4                                           TD D-882                                                                              MPa  37  38  38  38    40.5                                Yield point                                                                              MD D-882                                                                              MPa  15  17  17  23    21.6                                           TD D-882                                                                              MPa  14  15  15  21    20.7                                Elongation at Break                                                                      MD D-882                                                                              %    310 270 260 295 305                                              TD D-882                                                                              %    360 340 280 340 345                                   1% Secant modulus                                                                        MD D-882                                                                              MPa  210 215 390 380 380                                              TD D-882                                                                              MPa  200 225 380 350 345                                   Dart Drop impact                                                                            D-1709                                                                             g/micron                                                                             12.4                                                                              12.5                                                                              20.3                                        __________________________________________________________________________

It has been discovered that a golf ball can be generally produced inaccordance with the present invention from a central core and an outercover wherein the outer cover is made from a composition comprising ablend of about 5 to about 50 parts by weight of a thermoplastic rubberelastomer modified with maleic anhydride and/or other polar modifyinggroups, and about 95 to about 50 of an ionomeric resin based on 100parts by weight polymer in the composition.

More preferably, it has been found that a golf ball exhibited theproperties of enhanced playability and durability without sacrificingtraveling distance (i.e. C.O.R.) can be produced from a core and a coverwherein the cover is made from a composition comprised of about 15 toabout 40 parts by weight of a thermoplastic rubber elastomer modifiedwith maleic anhydride and/or other polar modifying group and about 85 to60 parts by weight of an ionomeric resin based on 100 parts by weightpolymer in the composition.

Most preferably, the golf ball of the present invention can be producedfrom a core and a cover wherein the cover is formed from a compositioncomprising 20 to 35 parts by weight of a thermoplastic rubber elastomermodified with maleic anhydride and/or other polar modifying groups andabout 80 to about 65 parts of an ionomeric resin based on 100 parts byweight polymer in the composition.

Additional materials may also be added to the compositions of thepresent invention, dyes (for example, Ultramarine Blue sold by Whitaker,Clark, and Daniels of South Plainsfield, NJ), titanium dioxide, UVabsorbers, antioxidants, and stabilizers. Moreover, the covercompositions of the present invention may also contain softening agents,such as plasticizers, etc., and reinforcing materials such as glassfibers and inorganic fillers, as long as the desired properties producedby the golf ball covers of the invention are not impaired.

The cover compositions of the present invention may be producedaccording to conventional melt blending procedures. Generally, thethermoplastic rubber elastomers modified with the polar groups, such asmaleic anhydride, are blended with the ionomeric resins in a Banburytype mixer, two-roll mill, or extruder prior to molding. The blendedcomposition is then formed into slabs and maintained in such a stateuntil molding is desired. If necessary, further additives such as aninorganic filler, antioxidants, stabilizers, and/or zinc oxide may beadded and uniformly mixed before initiation of the molding process.

Moreover, golf balls of the present invention can be produced by moldingprocesses currently well known in the golf ball art. Specifically, thegolf balls can be produced by injection molding or compression moldingthe novel cover compositions about wound or solid molded cores toproduce a golf ball having a diameter of about 1.680 inches and weighingabout 1.620 ounces. The standards for both the diameter and weight ofthe balls are established by the United States Golf Association(U.S.G.A.). Although both solid core and wound cores can be utilized inthe present invention, as a result their lower cost and superiorperformance, solid molded cores are preferred over wound cores.

Conventional solid cores are typically compression molded from a slug ofuncured or lightly cured elastomer composition comprising a high ciscontent polybutadiene and a metal salt of an α, β, ethylenicallyunsaturated carboxylic acid such as zinc mono or diacrylate ormethacrylate. To achieve higher coefficients of restitution in the core,the manufacturer may include a small amount of a metal oxide such aszinc oxide. In addition, larger amounts of metal oxide than are neededto achieve the desired coefficient may be included in order to increasethe core weight so that the finished ball more closely approaches theU.S.G.A. upper weight limit of 1.620 ounces. Other materials may be usedin the core composition including compatible rubbers or ionomers, andlow molecular weight fatty acids such as stearic acid. Free radicalinitiator catalysts such as peroxides are admixed with the corecomposition so that on the application of heat and pressure, a complexcuring or cross-linking reaction takes place.

The term "solid cores" as used herein refers not only to one piece coresbut also to those cores having a separate solid layer beneath the coverand above the core as in U.S. Pat. No. 4,431,193, and other multilayerand/or non-wound cores.

Wound cores are generally produced by winding a very large elasticthread around a solid or liquid filled balloon center. The elasticthread is wound around the center to produce a finished core of about1.4 to 1.6 inches in diameter, generally. Since the core material is notan integral part of the present invention, a detailed discussionconcerning the specific types of core materials which may be utilizedwith the cover compositions of the invention are not specifically setforth herein. In this regard, the cover compositions of the inventionmay be used in conjunction with any standard golf ball core.

As indicated, the golf balls of the present invention may be produced byforming covers consisting of the compositions of the invention aroundcores by conventional molding processes. For example, in compressionmolding, the cover composition is formed via injection at about 380° F.to about 450° F. into smooth surfaced hemispherical shells which arethen positioned around the core in a dimpled golf ball mold andsubjected to compression molding at 200°-300° F. for 2-10 minutes,followed by cooling at 50°-70° F. for 2-10 minutes, to fuse the shellstogether to form an unitary ball. In addition, the golf balls may beproduced by injection molding, wherein the cover composition is injecteddirectly around the core placed in the center of a golf ball mold for aperiod of time at a mold temperature of from 50° F. to about 100° F.After molding the golf balls produced may undergo various furtherprocessing steps such as buffing, painting, and marking.

The resulting golf balls produced from the novel ionomeric resin-polarmodified thermoplastic rubber elastomers exhibit enhanced playabilityproperties over the art without sacrificing distance and/or durability.This is because it is believed that the polar groups of the modifiedthermoplastic rubbers interact with the acid and ionic groups of theionomeric resins to produce compatible mixtures which, upon processing,are sufficiently soft to enhance playability but hard enough to maintainthe coefficient of restitution necessary for distance and durability.

The present invention is further illustrated by the following examplesin which the parts of the specific ingredients are by weight. It is tobe understood that the present invention is not limited to the examples,and various changes and modifications may be made in the inventionwithout departing from the spirit and scope thereof.

EXAMPLES

By blending the ingredients set forth in the Tables below, a series ofcover formulations were produced. In the examples, cover formulationscontaining thermoplastic rubber elastomers modified with a polar group,such as maleic anhydride, and a number of different types of ionomericresins were compared with unmodified thermoplastic rubberelastomer-ionomer resins. In addition, the properties produced by thecover compositions formulated with the unmodified and modifiedthermoplastic rubber-ionomeric resin blends were compared to theproperties produced by the cover materials representative of the TourEdition® (see Example 1) and the Top Flite® (see Example 2) ballscurrently being sold by Spalding & Evenflo Companies, Inc., Tampa,Florida. Although the specific formulations utilized to produce the TourEdition® and Top Flite® balls are proprietary, these formulations wereutilized under the same processing conditions as those set forth belowin order to produce covered golf balls for comparison purposes.

Along this line, the Tour Edition® ball is unique in that it is a twopiece solid core, molded cover ball that meets the needs of golfers whodemand superior control, historically obtained only with balata coveredwound balls. It offers superior playability at the sacrifice ofcoefficient of restitution, which relates directly to distance.

The Top Flite® ball is considered to be a "hard" Surlyn ionomeric resinball. As a result of the ball's hardness, the Top Flite® ball is adifficult ball for golfers to control. Generally, the harder the golfball, the more difficult it is for a golfer to impart spin to the ball,and hence, control the ball during flight. However, as a result of itsoutstanding durability and maximum distance, the ball is widely acceptedby a large percentage of golfers.

The present invention is directed to a blend of (1) a thermoplasticrubber elastomers modified with a polar group, such as maleic anhydride,and (2) an ionomeric resin, which, when utilized for golf ball covercompositions, produces golf balls possessing the superior playabilityproperties exhibited by the current Tour Edition® ball withoutsacrificing the coefficient of restitution (i.e. distance) associatedwith the Top Flite® ball. In addition, the cover compositions of thepresent invention exhibit enhanced durability over unmodifiedthermoplastic rubber-ionomeric resin compositions which possess some ofthe desired properties of the cover compositions of the presentinvention.

The cover formulations set forth below in Tables 5 and 6 were injectionmolded at 400° F. around identical solid type cores having a finisheddiameter of 1.545 inches to produce golf balls approximately 1.680inches in diameter having nominal cover thickness of 0.0675 inches. Theproperties of Riehle compression, coefficient of restitution (C.O.R.),Shore Hardness, impact resistance, and spin rate for the coverformulation were determined. In Tables 5 and 6, Examples 5 and 10 areidentical, and Examples 6 and 11 are similar (i.e. different unmodifiedthermoplastic rubbers are utilized) in composition. These Examples havebeen set forth for comparison purposes under two separate testingconditions. The data for each example represents the average data forone dozen balls produced according to the desired manner. The propertieswere measured according to the following parameters:

Riehle compression is a measurement of the deformation of a golf ball ininches under a fixed static load of 225 pounds.

Coefficient of restitution (C.O.R.) was measured by firing the resultinggolf ball is an air cannon at a velocity of 125 feet per second againsta steel plate which is positioned 12 feet from the muzzle of the cannon.The rebound velocity was then measured. The rebound velocity was dividedby the forward velocity to give the coefficient of restitution.

Shore hardness was measured in accordance with ASTM Test D-2240.

Cut resistance was measured in accordance with the following procedure:A golf ball is fired at 135 feet per second against the leading edge ofa pitching wedge, wherein the leading edge radius is 1/32 inch, the loftangle is 51 degrees, the sole radius is 2.5 inches, and the bounce angleis 7 degrees.

The cut resistance of the balls tested herein was evaluated on a scaleof 1-5. 5 represents a cut that extends completely through the cover tothe core; a 4 represents a cut that does not extend completely throughthe cover but that does break the surface; a 3 does not break thesurface of the cover but does leave a permanent dent; a 2 leaves only aslight crease which is permanent but not as severe as 3; and a 1represents virtually no visible indentation or damage of any sort.

The spin rate of the golf ball was measured by striking the resultinggolf balls with a 9 iron in the manner as described above wherein theclub-head speed is about 80 feet per second and the ball is launched atan angle of 26 to 34 degrees with an initial velocity of about 110-115feet per second.

The spin rate was measured by observing the rotation of the ball inflight using stop action Strobe photography.

Initial velocity is the velocity of a golf ball when struck at a hammerspeed of 143.8 feet per second in accordance with a test as prescribedby the U.S.G.A.

                                      TABLE 5                                     __________________________________________________________________________                1   2   3   4   5   6   7   8                                     __________________________________________________________________________    Ingredients                                                                   Kraton FG-1901X     15  --  30  --  22.5                                                                              --                                    Kraton G-2701                                                                             --  --  --  15  --  30  --  22.5                                  Surlyn 9910         18.8                                                                              18.8                                                                              15.1                                                                              15.1                                                                              17.0                                                                              17.0                                  Surlyn 8940 --  --  56.6                                                                              56.6                                                                              45.3                                                                              45.3                                                                              50.8                                                                              50.8                                  White MB             9.6                                                                               9.6                                                                               9.6                                                                               9.6                                                                               9.6                                                                               9.6                                  Properties                                                                    Melt Index                                                                    2160 g, 190 c                                                                 Weight, gms 45.5                                                                              45.5                                                                              45.4                                                                              45.5                                                                              45.4                                                                              45.5                                                                              45.5                                                                              45.5                                  Riehle Compression                                                                        51  49  43  47  49  48  47  49                                    C.O.R.      .802                                                                              .816                                                                              .811                                                                              .807                                                                              .805                                                                              .804                                                                              .809                                                                              .806                                  Shore A Hardness                                                                          90-91                                                                             98  94  95  91  91  92  92                                    Cut Resistance                                                                            2-3 2-3 2-3 2-3 3   5   2-3 3-4                                   (1 = Best, 5 = Worst)                                                         Spin Properties                                                               Launch Angle                27.6    28.4                                      Ball Speed                                                                    Spin Rate (RPM)             8626    8472                                      __________________________________________________________________________

                                      TABLE 6                                     __________________________________________________________________________                1   2   9   10  11  12  13  14  15                                __________________________________________________________________________    Ingredients                                                                   Kraton FG-1901X     --  30  --  --  30  --  --                                Kraton G-2706X      --  --  30  --  --  30  --                                Kraton RP-6510                                                                            --  --  --  --  --  30  --  --  30                                Surlyn 9910         --  15.1                                                                              15.1                                                                              15.1                                                                              --  --  --                                Surlyn 8940         --  45.3                                                                              45.3                                                                              45.3                                                                              --  --  --                                Iotek 4000          45.2                                                                              --  --  --  30.2                                                                              30.2                                                                              30.2                              Iotek 8000  --  --  45.2                                                                              --  --  --  30.2                                                                              30.2                                                                              30.2                              Surlyn White MB     --  9.6 9.6 9.6 --  --  --                                Iotek White MB      9.6 --  --  --  9.6 9.6 9.6                               Melt Index  1.6 2.8 4.8 0.66                                                                              2.9 1.0 1.3 6.1 2.5                               2160 g, 190 c                                                                 Weight, gms 45.7                                                                              45.6                                                                              45.7                                                                              45.3                                                                              45.5                                                                              45.3                                                                              45.4                                                                              45.3                                                                              45.4                              Riehle Compression                                                                        54  51  48  52  55  54  54  54  53                                C.O.R.      .792                                                                              .804                                                                              .809                                                                              .797                                                                              .795                                                                              .800                                                                              .802                                                                              .800                                                                              .803                              Shore C Hardness                                                                          87-88                                                                             95-96                                                                             96  87-88                                                                             86-87                                                                             87  89-90                                                                             88-89                                                                             88-89                             Cut Resistance                                                                            2-3 2-3 2-3 2-3 4-5 2-3 2-3 4-5 2-3                               (1 = Best, 5 = Worst)                                                         Spin Properties                                                               Launch Angle                                                                              30.0                                                                              31.8                                                                              32.6                                                                              29.7                                                                              29.8                                                                              30.2                                                                              30.4                                                                              30.7                                                                              30.4                              Ball Speed  113.2                                                                             112.7                                                                             112.8                                                                             114.6                                                                             114.1                                                                             113.8                                                                             113.6                                                                             113.7                                                                             113.8                             Spin Rate (RPM)                                                                           10117                                                                             8817                                                                              8066                                                                              10260                                                                             10218                                                                             10010                                                                             9706                                                                              9594                                                                              9679                              __________________________________________________________________________

DISCUSSION OF THE EXAMPLES

As indicated above, although blends of unmodified thermoplastic rubberswith ionomeric resins generally produce softer covers which exhibitenhanced playability, these covers have very poor durability. This isevident in Examples 6, 8, 11, and 14. In Examples 6 and 8, Kraton G-2701is blended with hard Surlyn grades 9910 and 8940 to produce relativelysoft covers (i.e. Riehle Compressions of 48 and 49 and C.O.R.s of 0.804and 0.806) in comparison to the hard Top Flite® cover composition setforth in Example 2 (i.e. the Top Flite® covers exhibit an averagecompression of 45 and an average C.O.R. of 0.816). The same can be seenin Examples 11 and 14 except Kraton G-2706X was utilized as theunmodified thermoplastic rubber. In addition, in Example 14, Iotek 4000and Iotek 8000 were substituted for the Surlyn ionomeric resins.

In this regard, significantly higher compressions, lower hardnessvalues, and lower C.O.R.s indicate that the balls would have a softerfeel and are thus, more readily deformed by a golf club. As a result ofthe additional deformation, a golfer can put more spin on the ball and,hence, impart better control over the ball.

However, while softer covers were produced by the unmodifiedthermoplastic rubber-ionomeric resin blends, the durability of thecovers also drastically decreased. This can be seen in the cutresistance values of 4-5. The results are very similar to those producedby balata covered balls. Thus, while the playability of the coversproduced from the unmodified thermoplastic rubber-ionomeric resin blendsincreased to some degree, the durability of the covers produced wasinsufficient for repetitive play.

Examples 5 and 7 in Table 5 and Examples 10, 12, 13, and 15 in Table 6involve cover formulations produced according to the present invention.Specifically, these examples involve covers produced from various polarmodified (i.e. maleic anhydride modified) thermoplastic rubber-ionomerresin blends. Example 12 is similar to Example 10 except Kraton RP-6510is used as the modified thermoplastic rubber elastomer as opposed toFG-1901-X. Examples 13 and 15 are similar to Examples 10 and 12respectively, except that the Surlyn ionomeric resins were substitutedwith Iotek ionomeric resins. The pigement concentrates were also changedto enhance compatibility.

The examples of the present invention (i.e. Examples 5, 7, 10, 12, 13,and 15) exhibit properties of enhanced playability demonstrated by theunmodified thermoplastic rubber-ionomeric resins without sacrificingdistance and/or durability. This can be seen in that the Riehlecompressions, Shore C hardness, and C.O.R.s of the covers of theformulations of the present invention are similar to the covers of theunmodified thermoplastic rubber-ionomeric resin formulations. Forexample, the values of the average Riehle compressions and C.O.R.s forExamples 5 and 7 are 48 and 0.807, respectively, and for Examples 6 and8 the values are 48.5 and 0.805 respectfully. These values are veryclose to the intermediate values produced by the combination of thedesired properties of the Tour Edition® ball (Example 1) and the TopFlite® ball (Example 2).

Furthermore, as demonstrated by the cut resistance results, thedurability of the cover compositions of the present invention (i.e. 2-3in Examples 5 and 7) is greatly improved over the unmodifiedthermoplastic rubber-ionomeric resin blends of Examples 6 and 8 (i.e.4-5). The same results can be seen in the comparison of Examples 10, 12,13 and 15 which are directed to the polar modified thermoplasticrubber-ionomer resin blends of the present invention versus Examples 11and 14 concerning the unmodified thermoplastic rubber-ionomer resinformulations.

In addition, in order to demonstrate that other maleic anhydridefunctionalized thermoplastic rubber elastomers sold under the "Kraton"trademark are also effective in the present invention, the aboveExamples were repeated with additional maleic anhydride modified Kratonrubbers. In this regard, Kraton RP-6510 contains about 0.5 weightpercent maleic anhydride, Kraton RP-5214 contains about 2.5 weightpercent maleic anhydride, and RP-6505 1.0 weight percent maleicanhydride. The results listed in Table 7 below demonstrate that theadditional maleic anhydride modified thermoplastic rubber elastomerswhen blended with ionomeric resins such as those sold under the Surlyn®designation offer higher coefficient of restitution (C.O.R.) than thecurrent Tour Edition® ball. See Examples 17-20.

In addition, the data set forth in Table 7, indicates that blends ofmaleic anhydride modified thermoplastic rubbers and unmodifiedthermoplastic rubbers produce increases in the coefficient ofrestitution (C.O.R.) over the current Tour Edition® ball. As mentionedabove, it is believed that the maleic anhydride modified thermoplasticrubber elastomers act as a compatibilizer between the unmodifiedthermoplastic elastomers and the ionomer resins.

                                      TABLE 7                                     __________________________________________________________________________              % MA                                                                              1  2  16 17 18 19 20 21                                         __________________________________________________________________________    Kraton FG-1901X                                                                         2.0       15.0                                                                             -- -- -- -- 15.0                                       Kraton 2706X                                                                            --        15.0                                                                             -- -- -- -- --                                         Kraton 1651                                                                             --  -- -- -- -- -- -- -- 15.0                                       Kraton RP-6510                                                                          .5        -- 30.0                                                                             -- -- -- --                                         Kraton RP-52-14                                                                         2.5       -- -- 30.0                                                                             -- -- --                                         Kraton RP-6505                                                                          1.0       -- -- -- 30.0                                                                             -- --                                         Kraton RP 6501                                                                          --  -- -- -- -- -- -- 30.0                                                                             --                                         Surlyn 9910                                                                             --        15.1                                                                             15.1                                                                             15.1                                                                             15.1                                                                             15.1                                                                             15.1                                       Surlyn 8940                                                                             --        45.3                                                                             45.3                                                                             45.3                                                                             45.3                                                                             45.3                                                                             45.3                                       White Masterbatch                                                                       --        9.6                                                                              9.6                                                                              9.6                                                                              9.6                                                                              9.6                                                                              9.6                                        Weight        45.6                                                                             45.4                                                                             45.6                                                                             45.3                                                                             45.4                                                                             45.4                                                                             45.3                                                                             45.7                                       Compression   57 52 55 54 54 56 55 54                                         C.O.R.        .807                                                                             .820                                                                             .810                                                                             .813                                                                             .811                                                                             .810                                                                             .811                                                                             .808                                       Shore C Hardness                                                                            83 87 82 84 85 83 85 84                                         Cut Resistance                                                                              2-3                                                                              2-3                                                                              2-3                                                                              2-3                                                                              2-3                                                                              2-3                                                                              2-3                                                                              2-3                                        (1 = No mark                                                                  5 = Clean cut)                                                                __________________________________________________________________________

As a result, the golf ball cover compositions of the present inventionproduces golf balls exhibiting properties of enhanced playabilitywithout sacrificing distance and/or durability.

The invention has been described with reference to the preferredembodiments. Obviously, modifications and alterations will occur toothers upon reading and understanding the preceding detaileddescription. It is intended that the invention be construed as includingall such alterations and modifications insofar as they come within thescope of the claims and the equivalents thereof.

Having thus described the preferred embodiments, the invention is nowclaimed to be:
 1. A golf ball comprising a core and a cover, wherein thecover is formed from a composition comprising from about 5 to about 50parts by weight of a maleic anhydride modified copolymer and from about95 to about 50 parts by weight of an ionomeric resin based on 100 partsby weight of the composition, wherein said maleic anhydride copolymerconsists of a copolymer selected from the group consisting of a maleicanhydride modified ethylene-propylene copolymer and a maleic anhydridemodified styrenic block polymer, and wherein said ionomeric resin is anionic copolymer of an olefin and a metal salt of an unsaturatedcarboxylic acid.
 2. A golf ball comprising a core and a cover, whereinthe cover is formed from a composition comprising from about 15 to about40 parts by weight of a maleic anhydride modified copolymer and fromabout 85 to about 60 parts by weight of an ionomeric resin based on 100parts by weight of the composition, wherein said maleic anhydridecopolymer consists of a copolymer selected from the group consisting ofa maleic anhydride modified ethylene-propylene copolymer and a maleicanhydride modified styrenic block polymer, and wherein said ionomericresin is an ionic copolymer of an olefin and a metal salt of anunsaturated carboxylic acid.
 3. A golf ball comprising a core and acover, wherein the cover is formed of a composition comprising fromabout 20 to about 35 parts by weight of a maleic anhydride modifiedcopolymer and from about 80 to about 65 parts by weight of an ionomericresin based on 100 parts by weight of the composition, wherein saidmaleic anhydride copolymer consists of a copolymer selected from thegroup consisting of a maleic anhydride modified ethylene-propylenecopolymer and a maleic anhydride modified styrenic block polymer, andwherein said ionomeric resin is an ionic copolymer of an olefin and ametal salt of an unsaturated carboxylic acid.
 4. A golf ball comprisinga core and a cover, wherein the cover is formed of a maleic anhydridemodified copolymer and an ionomeric resin, wherein said maleic anhydridemodified copolymer consists of a copolymer selected from the groupconsisting of a maleic anhydride modified ethylene-propylene copolymerand a maleic anhydride modified styrenic block copolymer, and whereinsaid ionomeric resin is an ionic copolymer of an olefin and a metal saltof an unsaturated carboxylic acid.